CN102841279A - Micro-grid island detection method - Google Patents

Abstract

The invention relates to the field of protection and control of micro-grids of electric power systems and particularly relates to a micro-grid island fast detection method. The method is sued for an inverter-based distributed generation (IBDG) with a PQ (power quest) decoupling control strategy; a corresponding reactive power control strategy is adopted in the method on the basis of measuring a voltage effective value UPCC and the load reactive power of a common coupling point PCC in real time through comparing the voltage effective value UPCC with the voltage effective value under a normal condition; when island determination is performed, firstly, a voltage threshold value and a frequency threshold value are predetermined, the voltage effective value UPCC is compared with the voltage threshold value, if the voltage effective value UPCC exceeds the threshold value, the PCC is directly determined be in an island state and the island detection is finished, and if the voltage effective value UPCC does not exceed the threshold value, the voltage frequency f of the PCC is compared with the frequency threshold value, the PCC is determined to be in the island state if the voltage frequency f of the PCC exceeds the threshold value. With the adoption of the detection method, the micro-grid island detection can be realized fast, and the effectiveness of the island detection can be ensured even under the existence of a plurality of inverter-based distributed generations.

Description

A kind of little electrical network island detection method

Technical field

The present invention relates to little electric network protection of electric system and control field, relate to a kind of little electrical network island detection method.

Background technology

To be little electrical network change the prerequisite of islet operation into by unplanned isolated island to little electrical network island detection, and important effect is being disposed in the control strategy and the protection that change in little electrical network.For contingent island effect; The relevant criterion that IEEE (IEEE) formulates is the employed island detection method of specific requirement no longer; But be conceived to the performance index of island detection method in the island detection process, thereby guided the development trend of island detection standard.Existing island detection method can be divided into passive detection method, active detecting method and on off state monitoring method three major types.Wherein, Passive detection method can not impact the system power quality, but when unplanned isolated island takes place, if the output power of distributed power source (DG) and the electric energy of load consumption are more or less the same; Then point of common coupling (PCC) is located voltage, frequency etc. within the permission variation range; This method can't detect isolated island, have bigger detection blind area, combine utilization usually with the active detecting method.The active detecting method is through introducing disturbing signal in the control signal of inverse type DG; And the response of electric parameters such as monitoring PCC place voltage, frequency; Judge whether unplanned isolated island takes place, and this method has reduced the detection blind area, but also the quality of power supply has been caused certain influence simultaneously.In addition, when the active detecting method is applied to a plurality of DG,, then can reduce the validity of method if the system responses that disturbing signal produces is asynchronous.The on off state monitoring method is through detecting the state that cut-offs of power distribution network side isolating switch; And this signal being sent to the operational mode that DG judges little electrical network based on mechanics of communication, this method does not exist and detects the blind area, does not influence the quality of power supply yet; But realize comparatively complicated, less economical.

The present invention is through the control to inverse distributed power (IBDG) output reactive power; A kind of new departure that can the little electrical network island detection of Rapid Realization has been proposed; This scheme does not detect the blind area, under the situation of a plurality of IBDG, still can guarantee the validity of island detection, and when little electrical network is incorporated into the power networks; Through the dynamic passive compensation of IBDG, can improve the system voltage quality.

Summary of the invention

The objective of the invention is to overcome the above-mentioned deficiency of prior art; Provide a kind of can the little electrical network island detection method of Rapid Realization; This method does not detect the blind area, under the situation of a plurality of IBDG, still can guarantee the validity of island detection, and when little electrical network is incorporated into the power networks; Through the dynamic passive compensation of IBDG, can improve the system voltage quality.Substantive distinguishing features of the present invention is: through taking the idle control strategy of appropriate IBDG; When unplanned isolated island takes place in little electrical network; Idle and meritorious not matching causes PCC place frequency to continue skew towards same direction jointly, until exceeding threshold value, thereby realizes quick island detection.Technical scheme of the present invention is following:

A kind of little electrical network island detection method is used to adopt the inverse distributed power IBDG of PQ decoupling control policy, and this method is measured the point of common coupling PCC voltage effective value U of place in real time _PCCAnd load reactive power Q _LoadThe basis on, through U relatively _PCCWith voltage effective value U under the normal condition _NSize cases, take the idle control strategy of corresponding IBDG, if U _PCCMore than or equal to U _N, the reactive power that IBDG output then is set does

Otherwise, if U _PCCLess than U _N, the reactive power that IBDG output then is set does

F is a PCC place electric voltage frequency in the formula, k ₁And k ₂Be the regulated variable in the idle control strategy;

Carrying out isolated island when judging, at first predeterminated voltage threshold value and frequency threshold value, and with U _PCCCompare with the voltage threshold value,, then directly be judged to be island state, finish the island detection of epicycle if exceed threshold value; Otherwise, measure the PCC electric voltage frequency f of place, measured frequency f and frequency threshold value are compared, if exceed threshold value, then be judged to be island state.

The present invention compared with prior art; A kind of quick island detection method of little electrical network that improves the quality of voltage ability that has has been proposed; The good effect that this method can produce is: at first; The present invention has considered to gain merit and idle not matching when unplanned isolated island takes place simultaneously, adopts active and passive island detection method to combine, and has guaranteed that there is not the detection blind area in this method; Secondly; The present invention during according to isolated island meritorious not matching take the idle control strategy of appropriate IBDG, make the frequency shift (FS) direction consistent, until exceeding allowed band; Therefore can the Rapid Realization island detection, so that in time change the control strategy and protection configuration in little electrical network; The present invention can also carry out reactive-load compensation according to the system voltage state when little electrical network is incorporated into the power networks, can improve quality of voltage, and when distribution network failure etc. causes that system voltage reduces, makes DG have stronger low voltage ride-through capability; At last, the present invention is equally applicable to the situation that a plurality of IBDG move simultaneously, has guaranteed the validity of detection method.

Description of drawings

Fig. 1 is standard isolated island test macro main circuit topology figure;

Fig. 2 is the PQ decoupling zero control block diagram of inverse type DG (IBDG);

Fig. 3 a is the regularly idle graph of a relation with system frequency of load of PCC place voltage one;

Fig. 3 b is at the enlarged drawing at required research section 49.3Hz ~ 50.5Hz place among Fig. 3 a;

Fig. 3 c is the regularly meritorious graph of a relation with system frequency of load of load idle;

Fig. 4 a is the graph of a relation of PCC place voltage idle and frequency idle with frequency and IBDG of load during more than or equal to 220 volts;

Fig. 4 b is the graph of a relation of PCC place voltage idle and frequency idle with frequency and IBDG of load during less than 220 volts;

Fig. 5 is the process flow diagram of the quick island detection method of little electrical network of carrying.

Embodiment

To combine embodiment below and be elaborated with reference to the technical scheme of accompanying drawing to this invention.

The present invention is through adopting the appropriate idle control strategy of inverse type DG; Take all factors into consideration meritorious and idle not the matching that possibly exist when unplanned isolated island takes place; A kind of quick island detection method of little electrical network that can improve the quality of voltage ability that has is provided; This method does not exist and detects the blind area, validity that still can ensuring method under the situation that a plurality of IBDG move simultaneously.

1. be directed against isolated island test macro and the PQ decoupling control policy of inverse type DG

According to the difference of the method for operation, distributed power source generally can be divided into tradition rotation type DG and inverse type DG (IBDG).Wherein, IBDG is parallelly connected with electrical network through power electronic equipment, is the principal mode that present DG is incorporated into the power networks, and the standard isolated island test macro of distributed power source of stipulating among IEEE Std.929-2000 and the UL1741 and combining inverter is as shown in Figure 1.Under the pattern of being incorporated into the power networks, IBDG links to each other with power distribution network through point of common coupling (PCC), and simultaneously for load provides power, the relational expression between meritorious and the idle and load equivalent impedance of load consumption is respectively With $Q_{\mathrm{Load}}=Q_{\mathrm{DG}}+\mathrm{\Δ\; Q}=3V_{\mathrm{PCC}}^2(\frac{1}{2\mathrm{\π\; FL}}-2\mathrm{\π\; FC}),$ V wherein _PCCBe the voltage at PCC place, f is the frequency of PCC place voltage.When switch opens shown in Fig. 1, IBDG and load form isolated island, and the required electric energy of load is provided by IBDG fully.Therefore, can know by the above-mentioned relation formula: if IBDG output meritorious be during greater than load consumption meritorious, V _PCCTo increase, otherwise, V _PCCTo reduce; And meritorious all will cause the variation of f with idle not matching, when IBDG provide idle when equaling load consumption idle, if it provides meritorious meritorious greater than load consumption then will cause the rising of f, otherwise, will make f reduce; When IBDG provide meritorious when equaling load consumption meritorious, if it provides idle idle greater than load consumption then will cause the reduction of f, otherwise, will make f raise; When IBDG provides when all not matching with load consumption meritorious and idle, the variation of f will be determined with the idle degree that do not match by meritorious jointly.In sum, when unplanned isolated island took place, the degree that do not match was enough big if IBDG provides power with load consumption, can cause that then PCC place voltage and frequency exceed allowed band, thus the realization island detection, otherwise, will get into the detection blind area.

Based on instantaneous power theory; IBDG adopts the PQ decoupling control policy; Thereby can realize the idle control strategy to IBDG, idle not matching causes that frequency exceeds threshold value to realize island detection during through isolated island, and the control block diagram of PQ decoupling control policy is as shown in Figure 2; Comprise phaselocked loop, power outer shroud and current inner loop [1,2].Through introducing the three-phase voltage at PCC place, phaselocked loop can provide the voltage phase angle of realizing synchronous Parker conversion, and can calculate the frequency of PCC place voltage.In the power outer shroud,, meritorious and idle reference value and the error between the real power are modulated to the reference value of the meritorious and idle component of inverter output current respectively through one group of proportional integral (PI) regulator.Current inner loop realizes the decoupling zero control to the meritorious and idle component of inverter output current, by the formula of inverter output power then through the feedforward control algorithm

With

Can know that the adjusting through to the meritorious and idle component of output current can realize its meritorious and idle independent control, and reach the reference value P that sets _RefAnd Q _Ref[2,3].

The source of the list of references that relates in the above-mentioned paragraph is following:

[1] Tian Xiaohe, the control and the protection of light storage commingled system: [master thesis], Tianjin: University Of Tianjin, 2011.

[2]Zeineldin?H.H.A?Q-f?droop?curve?for?facilitating?islanding?detection?of?inverter-based?distributed?generation.IEEE?Transactions?on?Power?Electronics,2009,24(3):665-673.

[3]Schauder?C,Mehta?H.Vector?analysis?and?control?of?advanced?static?VAR?compensators.IEE?Proceedings?C,1993,15(3):299-306.

2. has the quick island detection method of little electrical network that improves the quality of voltage ability

In traditional P Q decoupling control policy, the reference value Q that IBDG output is idle _RefUsually be set at zero, promptly IBDG moves according to unity power factor, so that improve the operational efficiency of inverter to greatest extent.Yet the fluctuation that the load of PCC place is idle will produce the place's of being incorporated into the power networks voltage and have a strong impact on.Therefore, under the situation that little electrical network is incorporated into the power networks, through the PQ decoupling control policy; IBDG can carry out reactive-load compensation to load; Reduced power distribution network to PCC place load provide idle, improved the power factor of load, reduced simultaneously and to have carried the idle voltage landing that causes.But when unplanned isolated island took place, IBDG carried out reactive-load compensation to load, has reduced idle degree of not matching, and had added the detection blind area thereby increase.Therefore, must take the idle control strategy of appropriate IBDG, reach and under the situation of being incorporated into the power networks, to improve quality of voltage, can realize the effect of quick island detection again.

Fig. 3 a is depicted as the regularly idle graph of a relation with system frequency of load of PCC place voltage one, and Fig. 3 b is depicted as among Fig. 3 a the enlarged drawing at required research section 49.3Hz ~ 50.5Hz place.Can know by figure, when PCC place voltage one regularly, load is idle and the graph of a relation approximately linear of system frequency, and load is idle reduces along with the increase of frequency.Fig. 3 c is depicted as the regularly meritorious graph of a relation with system frequency of load of load idle, can know by figure, when load idle regularly, load is meritorious to increase along with the increase of frequency.In addition,, can draw through deriving because IBDG is constant power source, meritorious when unplanned isolated island takes place between IBDG and the load do not match and the idle frequency shift (FS) that does not match respectively and cause between relation.When the idle coupling between IBDG and the load; Meritorious do not match and the relational expression of the frequency shift (FS) that it causes is: is when the meritorious coupling between IBDG and the load; The relational expression of the idle frequency shift (FS) that causes with it of not matching is: in

formula; Δ P and Δ Q are respectively meritorious and the idle amount of not matching; P and Q are the meritorious and idle value of load; L and C are respectively the equivalent inductance and the equivalent capacity of load; F is a PCC place electric voltage frequency before isolated island takes place, and Δ f is the frequency shift (FS) that power does not match and causes.Comprehensive above-mentioned bearing power and system frequency graph of a relation and the derivation of equation can be known; When isolated island takes place; IBDG provides meritorious and idle respectively simultaneously greater than or required when meritorious and idle less than load simultaneously; Meritorious and the idle degree of not matching will cause that frequency changes to different directions, thereby reduce island detection speed, even get into the island detection blind area.Therefore, the IBDG that is taked is idle control strategy needs with the meritorious foundation as a reference that do not match, and makes when isolated island takes place meritorious and idle not matching cause that frequency increases simultaneously or reduces, thereby realizes quick island detection.Because when isolated island takes place, meritorious not matching will directly cause the variation of PCC place voltage again, so in this programme, the idle control strategy of IBDG is with the variation of the PCC place voltage of easier detection foundation as a reference.

Simultaneously; Because the variation range that the normal runtime system frequency of system allows is 49.3Hz ~ 50.5Hz; In order to eliminate the island detection blind area; Idle not matching need perseverance exist in the frequency allowed band, promptly within the frequency allowed band, has deviation between the relation curve of the idle and frequency of the relation curve of the idle and frequency of IBDG and load.In this programme, the idle control strategy of IBDG with the 49.2Hz that exceeds the frequency allowed band and 50.6Hz respectively as PCC place voltage raises and make IBDG and the idle equal frequency node of load when reducing when detecting.

Comprehensive above-mentioned two aspect contents, the idle control strategy of IBDG is:

A. when PCC place voltage effective value during more than or equal to 220 volts,

$Q_{\mathrm{DG}}=-{10}^{k_1}(f-49.2)+Q_{\mathrm{Load}}$

B. when PCC place voltage effective value during less than 220 volts,

$Q_{\mathrm{DG}}=-{10}^{k_1}(f-50.6)+Q_{\mathrm{Load}}$

K in the formula ₁Be regulated variable, can set its value according to IBDG capacity etc., and numerical value be big more, the idle degree that do not match between IBDG and the load is big more, thereby the island detection time is also short more.Load under above-mentioned two kinds of situation is idle with frequency relation curve and IBDG idle with the frequency relation curve respectively shown in Fig. 4 a and Fig. 4 b.

To the idle control strategy of above-mentioned IBDG; When isolated island takes place; Meritorious not matching can cause that PCC place voltage effective value is greater than or less than 220 volts of voltage effective values under the normal condition between IBDG and the load; And then take corresponding idle control strategy, and make that the idle change of frequency direction that causes that do not match between IBDG and the load is consistent with the meritorious change of frequency direction that causes that do not match, realize quick island detection.Under the situation of being incorporated into the power networks, when PCC place voltage was higher, what IBDG sent was idle idle less than load, thereby power distribution network provides the idle PCC of making place voltage to reduce to load; When PCC place voltage was on the low side, what IBDG sent was idle idle greater than load, thereby recovered to the idle PCC place voltage that makes of power distribution network input.Promptly under the situation of being incorporated into the power networks, the idle control strategy of being taked makes IBDG be equivalent to reactive power compensator, can improve PCC place quality of voltage.But in the idle control strategy of above-mentioned IBDG, the degree of not matching idle during power frequency is fixed; Improvement degree to PCC place quality of voltage is limited, and can not realize dynamic improvement, therefore; Through introducing PCC place magnitude of voltage, the idle control strategy of above-mentioned IBDG is improved as follows:

A. when PCC place voltage effective value during more than or equal to 220 volts,

$Q_{\mathrm{DG}}=-{10}^{k_1+\left(\frac{U_{\mathrm{PCC}}-U_N}{U_N}\right)\×k_2}(f-49.2)+Q_{\mathrm{Load}}$

B. when PCC place voltage effective value during less than 220 volts,

$Q_{\mathrm{DG}}=-{10}^{k_1+\left(\frac{U_N-U_{\mathrm{PCC}}}{U_N}\right)\×k_2}(f-50.6)+Q_{\mathrm{Load}}$

U in the formula _PCCBe PCC place voltage effective value, U _NBe 220 volts of the voltage effective values under the normal condition, k ₂Be regulated variable.At this moment, not only can be under the situation of being incorporated into the power networks realize dynamically improving PCC place quality of voltage, and not matching of gaining merit when taking place of isolated island can further strengthen idle not matching, thereby further improve island detection speed through dynamic passive compensation.

When isolated island took place, meritorious not matching can cause the variation of PCC place voltage between IBDG and the load, though there is the blind area in the OVP/UVP method, when the meritorious degree that do not match is enough big, can judge directly that isolated island takes place.Therefore, idle control strategy of comprehensive above-mentioned IBDG and OVP/UVP method, OFP/UFP method form the quick island detection method of little electrical network that as shown in Figure 5 having improves the quality of voltage ability.The concrete steps of this scheme are:

The first step: measure the voltage effective value U of PCC place in real time _PCCAnd the idle Q of load _Load

Second step: with U _PCCCompare with the voltage threshold value in the passive detection method OVP/UVP method.If exceed threshold value, then directly be judged to be island state; Otherwise, change next step over to.

The 3rd step: measure the PCC electric voltage frequency f of place.

The 4th step: measured frequency f and frequency threshold value are compared.If exceed threshold value, then be judged to be island state; Otherwise, change the first step over to.

Above-mentioned threshold value can be set with reference to threshold value in the passive detection method OFP/UFP method.

There is not the detection blind area in the quick island detection method of above-mentioned little electrical network; Detection speed is fast; Detection time is less than short weight closing time; Can avoid unsuccessful reclosing that distributed power source and other system equipments are worked the mischief, and under the situation of being incorporated into the power networks, can improve quality of voltage through dynamic passive compensation.Simultaneously, this scheme not only has above-mentioned superperformance under single IBDG situation, and is applicable to the situation of a plurality of IBDG fully.

Above content is merely embodiments of the invention, and its purpose is not the restriction that is used for system and method proposed by the invention, and protection scope of the present invention is as the criterion with claim.Under the situation that does not break away from the spirit and scope of the present invention; Those skilled in the art all should drop within protection scope of the present invention its all conspicuous modification or variation about form and details of carrying out under the situation that does not depart from scope of the present invention and spirit.

Claims (1)

1. little electrical network island detection method is used to adopt the inverse distributed power IBDG of PQ decoupling control policy, and this method is measured the point of common coupling PCC voltage effective value U of place in real time _PCCAnd load reactive power Q _LoadThe basis on, through U relatively _PCCWith voltage effective value U under the normal condition _NSize cases, take the idle control strategy of corresponding IBDG, if U _PCCMore than or equal to U _N, the reactive power that IBDG output then is set does

Otherwise, if U _PCCLess than U _N, the reactive power that IBDG output then is set does

F is a PCC place electric voltage frequency in the formula, k ₁And k ₂Be the regulated variable in the idle control strategy;

Carrying out isolated island when judging, at first predeterminated voltage threshold value and frequency threshold value, and with U _PCCCompare with the voltage threshold value,, then directly be judged to be island state, finish the island detection of epicycle if exceed threshold value; Otherwise, measure the PCC electric voltage frequency f of place, measured frequency f and frequency threshold value are compared, if exceed threshold value, then be judged to be island state.

Images